The grammatical question would be better asked on French. As far as my understanding goes, single adjective signs are often in the default masculine form, similar to the generic demonstrative form "c'est occupé", although it is not wrong to use the feminine form, as in "la toilette est occupée".

“Occupé” refers to the bathroom. A French speaker would choose a gender marker based on the word used (implicitly) to refer to it (e.g. “la salle de bain est occupée” or “le bureau est occupé”). The gender of the person in it is linguistically irrelevant so the second tweet quoted is completely off-base.

Can't she just fly Delta rather than Air Senegal?

@Berend The plane was already shown on thursday's comic: grrlpowercomic.com/archives/comic/… Not sure what livery that is, but I don't think that's Delta.

@Relaxed it may be off base, but it's not completely so, for it is indeed possible to occupy a space in a masculine or feminine way by virtue of being masculine or feminine; it's just that this is not reflected in the word occupé(e) but instead in the word occupant(e). N'est-ce pas ? (Okay, maybe it's a bit generous to make the stretch from the gender of an occupant to the manner in which the occupant occupies something, but it's at least far closer than the incorrect association between the gender of the thing being occupied and the manner of occupying it.)

@xngtng “La toilette” is not a way any French person would describe toilets (there’s a completely different use for the singular version though). It would either be “les toilettes” (feminine plural), les WC (masculine plural), maybe “la cabine” (feminine singular), but it’s a lot more likely to be just “occupé” as in “c’est occupé”.

@phoog in French the article or adjective takes the gender of the noun, whereas in English it takes the gender of the possessor. Since “toilette” is feminine as a noun, it will be “occupée” with feminine termination. Using “occupe” would imply that the gentleman is occupied, not the washroom.

@ZeroTheHero in fact, see my comment on xngtng's answer, since the place where you pee is not "la toilette" but "les toilettes," and, despite that fact, the sign always says "occupé," not "occupées," because there is no specific noun which which the adjective must agree.

@phoog then it should be “occupées” feminine plural.

@ZeroTheHero but it isn't, because using an adjective for something when it isn't clear what noun you're thinking of (is it "le WC" or "les toilettes" or "l'espace des toilettes" or something else?) defaults to masculine.

@ZeroTheHero wait, what are you talking about? Articles and adjectives don't take any gender in English. Possessive pronouns reflect the gender of the possessor, but they aren't declined per se; they're different words, as are "he" and "she." In the days before English lost grammatical gender -- and still today in German -- possessive pronouns reflected both the gender of the possessor and of the thing possessed.

@phoog “her book” if the possessor is a woman; “his book” is the possessor is a man. “Le livre” irrespective of the possessor in French.

Incidentally, “occupied” seems like an odd choice in English. It's not wrong but I suspect “busy” or “closed” would be more idiomatic.

@Nzall It isn't Delta, but it isn't Air France, either. Looks like just some generic livery, not any actual airline. Also, you're correct to not post this on Aviation.SE. Things having to do with passenger cabins generally don't belong there, unless it's something to do with safety (e.g. evacuation, structural testing requirements, fire hazards, etc.)

@Relaxed "Occupied" is the normal word to use on bathrooms in English when they're in use. At least for AmE, but, AFAIK, this is also true for BrE. "Closed" would mean that they're out-of-service for some reason (e.g. needs cleaning, cleaning in progress, inoperative, etc.) "Busy" would get the point across, but isn't really idiomatic for the situation.

@ZeroTheHero The English translation of "le livre" is just "the book," which isn't gendered. Articles and normal adjectives aren't gendered at all in English, but personal pronouns are.

@reirab fair enough. “son livre” would be always masculine even if it is her book.

@reirab in BrE, "engaged" is paired with "vacant", for example on locks with an indicator. "Occupied" is also seen, and seems more common when the other state is blank or a word other than "vacant" is used ("available", for example)

I’m voting to close this question because it is actually a language question, but with the current amount of activity it feels wrong to migrate the question.

@ZeroTheHero in Germanic languages the choice of possessive pronoun depends on the gender of the possessor, but the pronoun itself is declined according to the gender of the thing possessed. In German, for example, ihr Buch, sein Buch (neuter) and ihr Stuhl, sein Stuhl (masculine) but ihre Tasse, seine Tasse (feminine).

In English, the declination of the pronoun is null, so only the choice of his or her (or its) remains. But that's not the same as declining the pronoun according to the possessor's gender.